Liquid crystal display devices are commercially well-known. Furthermore, in recent years, mobile devices are used in increasingly wide purposes. As such mobile devices, smartphones with liquid crystal display devices are well known, for example. As to such liquid crystal display devices, improvement of display quality is in great demand to achieve higher definition, higher color purity, and higher brightness of the display. Furthermore, lower energy consumption is also in great demand to achieve a longer battery drive.
In order to satisfy the above contradictory demands for achieving the higher color purity, higher brightness, and lower power consumption at the same time, research and development of liquid crystal display devices using a pixel structure of four color pixels: red, green, blue, and white (RGBW) are keen to substitute an ordinary pixel structure of three color pixels: red, green, and blue (RGB).
However, when using a so-called RGBW stripe pixel structure (in which columns of four pixels of RGBW extending linearly are arranged in a row direction), each pixel has a slender shape which causes a significant decrease in display uniformity. To solve such a problem of the decrease in display quality, a so-called RGBW square pixel structure (in which four pixels of RGBW are arranged in a square) is under development.
Here, comparing the RGBW square pixel structure to the RGBW stripe pixel structure, the number of pixels arranged in each column of the RGBW square pixel structure is twice that of the RGBW stripe pixel structure. That is, the number of scanning lines of the RGBW square pixel structure is twice as much, too. What should be noted here is a writing time. The writing time of image signals from signal lines to pixels varies depending on the number of scanning lines, and the time must be shortened proportionately if the number of scanning lines increases. The resolution in the horizontal direction can be improved by simply increasing the number of signal lines and it has no effect on the writing time. However, when higher definition of display performance and greater frame frequency are aimed, reduction of the writing time of image signals is inevitable. As a result, a writing time of image signals will become insufficient and energy consumption in a driving circuit will increase significantly due to the increase of driving frequency.
In consideration of the above, there is a technique under development which provides one scanning line per row of RGBW square pixels while providing two signal lines per column of RGBW square pixels. That is, four pixels of an RGBW square pixel share a single scanning line. With this technique, even when the RGBW square pixel structure is used and the driving frequency is increased, a sufficient writing time of image signals can be secured. Furthermore, the energy consumption in a driving circuit can be suppressed, thereby to achieve lower power consumption.
However, when two signals lines are provided per one column on which pixels are aligned, the coupling capacitance produced between neighboring signal lines may increase to produce noise on the signal lines. The noise on a signal line undesirably varies the voltage value on the image signal applied to the signal line, creating an error in the voltage value. This causes the degradation of display quality.